When the reception system is restricted instantaneous band (for example of the order of several hundred MHz), this signifies that the N reception channels corresponding to the N antennas of the array must perform a frequency sweep over time so as to fully scan the entirety of the required frequency coverage.
These multichannel reception systems with or without restricted instantaneous band, are particularly suited for performing goniometry. They are capable of measuring the direction of arrival of a given incident wave. A particular feature of the incident wave may be brevity, for example pulse-amplitude-modulated signals with a relatively low shape factor (such as those emitted by radars). It is then appropriate to be able to perform the goniometry in a very short time, and therefore, to measure the set of signals delivered by the goniometric antenna array very rapidly and in parallel.
Accordingly, the aforementioned multichannel reception systems advantageously comprise a receiver produced on the basis of arrays of antennas:
either off-boresighted (array of directional antennas generally equidistributed in angle in the plane of measurement of the direction of arrival of the incident waves), said receiver is then coupled to a measurement means able to use the power of the signals delivered by the antenna array,or delocalized (antenna array which is generally locally linear and sparse in the plane of measurement of the direction of arrival) and said receiver is then coupled to a measurement means able to use the distribution of path length differences which arises from the antenna array.
Of course, these examples are not limiting.
An instantaneous wideband multichannel reception system (here N channels), can therefore acquire N signals arising from the N antennas of the array.
Accordingly, it is furnished with as many amplitude analyzers as channels, so as to measure the power of the incident wave on each channel. The distribution of these powers over the N channels makes it possible to calculate a direction of arrival parameter, calculated by virtue of a so-called amplitude goniometry estimator.
Furthermore, the technical analysis of the signal requires the measurement of its frequency, the latter being the same on each channel and for the sake of simplification, a single frequency meter is generally used. Under these conditions, a combining means is employed, the role of which is to deliver just a single signal on the basis of the N, to the lone frequency meter.
Today, this combiner function takes various rather unsatisfactory forms. It may involve a simple microwave coupler with N input channels. This has the defect of effecting the vector addition of N channels with non-controllable phases. The consequence is that the signal output by said combiner may be cancelled out through phase opposition of the input signals. As a variant, it may involve systems mixing the coupling of certain channels and the multiplexing of the coupled outputs by switching. This solution has the defect of affecting the integrity of the signal.
It is noted that the aforementioned multichannel reception systems may furthermore possess means able to perform a frequency resolution of the signals received by the antennas. One then speaks of a reception system with spectral analysis of restricted instantaneous band, this restriction being effected by reception chains of superheterodyne type.
A disadvantage of the instantaneous wideband multichannel reception systems (no frequency resolution) described hereinabove is the amount of hardware required (an amplitude analyzer per channel) and therefore the bulkiness, the cost of the system to a certain extent. Moreover, the aforementioned combiner function induces numerous technical snags.
Another major disadvantage of the spectral analysis multichannel reception systems of the prior art is the amount of hardware (a spectral analyzer per channel) and therefore the bulkiness and the cost of the system.